Expanded polystyrene bead having functional skin layer, manufacturing process thereof, and functional EPS product and manufacturing process thereof using the same

ABSTRACT

Expanded polystyrene particles having a polyvinyl acetate resin-based functional skin layer, and a process thereof are provided. The particle includes an inner expanded polystyrene layer; and a functional skin layer. The inner expanded polystyrene layer is formed by heating and expanding an expandable polystyrene bead or pellet, and the functional skin layer is formed by coating the surface of the inner expanded polystyrene layer with a functional coating composition having 10 to 99 wt % of a vinyl acetate based polymer and 0.1 to 90 wt % of at least one functional additive.

TECHNICAL FIELD

The present invention relates to expanded polystyrene molded productshaving various functions, including flame-retardation, antibacterialproperties, coloration properties, etc. More particularly, the presentinvention relates to (pre-) expanded polystyrene particles having afunctional skin layer produced by coating the surface of (pre-) expandedpolystyrene particles with a functional coating composition, a processfor producing the expanded polystyrene particles, functional expandedpolystyrene molded products manufactured using the expanded polystyreneparticles with a functional skin layer, and a process for manufacturingthe polystyrene molded products.

BACKGROUND ART

Expanded polystyrene is a polymer resin obtained by heating and curingthe expandable polystyrene resin including expanding agent, such aspentane (C₅H₁₂) or butane (C₄H₁₀) in polystyrene resin or its copolymerresins, to generate foams therein. Expanded polystyrene is white incolor, light in weight, and is superior in water resistance, thermalinsulation properties, sound absorption and buffering properties. Due tothese advantages, expanded polystyrene resin is widely used as apackaging material, a construction material, a material for floats, lifejackets, decorative articles, insulators, living products, such as foodcontainers and disposable products, and the like.

More detailed explanation regarding a molding process of expandedpolystyrene products will be described below. A polystyrene or styrenecopolymer resin containing an expanding agent in the shape of a beadhaving a diameter 0.2˜0.3 mm or a pellet having a length of about 2.5 mmis pre-expanded to produce expanded particles (usually in the forms ofbeads). Thereafter, the expanded particles are aged and dried. The agedexpanded particles are placed in a mold, heated with a high-pressuresteam, and thus molded into a desired shape.

The expanded polystyrene thus produced contains 98 vol % of air and onlyabout 2 vol % of the polymer resin. Further, the expanded polystyrenehas a unique expanded structure in which air is enclosed by plasticfoams. Based on this structure, since the expanded polystyrene islightweight and shows superior buffering properties, thermal insulationproperties, and sound absorption, it can be widely utilized in manyapplications.

However, since the expanded structure makes the expanded polystyrenemore susceptible to some chemicals than the chemical resistance inherentto the polystyrene resin, the expanded structure is an obstacle inimparting a variety of functions upon the expanded polystyreneparticles.

That is, the addition of functional components to expanded polystyrenesin order to impart additional functions to expanded polystyrene productspresents difficulties that water resistance and heat resistance of thefunctional components, and moldability and chemical resistance of theexpanded polystyrene must be comprehensively taken into account.Accordingly, functional expanded polystyrene molded products hithertodeveloped are very limited in the selection of the amount and kind offunctional components within the range that does not affect physical andchemical properties during preparation of polystyrene.

Particularly, since expanded polystyrenes have relatively low meltingpoint, and the molten polystyrene has low viscosity, molded productsmade of expanded polystyrene lose their structure and are melted easilyby fire, thus being converted to a combustible liquid material. Underthese circumstances, regulations including the Fire Services Act, inmost developed countries, restrict the use of expanded polystyrenes,which prohibits the development of the expanded polystyrenes asconstruction materials.

In order to solve these problems, great efforts have been devoted todeveloping flame-retardant or fire-resistant expanded polystyrenes. Forexample, U.S. Pat. No. 6,384,094 discloses a process for preparing afire-resistant expandable polystyrene by adding 1˜12 wt % of anexpandable graphite or an expanded graphite to a suspension containing astyrene monomer. In addition, the patent publication proves theusefulness of the expandable polystyrene thus prepared.

However, the expandable graphite begins to expand at about 900° C.,whereas the polystyrene leaves 3 wt % of ash behind at 500° C. or abovebecause of its extremely low heat resistance. The expandable graphite isexpanded upon high-temperature heating to perform its thermalinsulation, but the graphite loses its structure due to the absence of amaterial capable of binding the graphite, resulting in poor fireresistance.

On the other hand, Korean Utility Model No. 323680 describes aflame-retardant expanded polystyrene panel manufactured by coating anaqueous sodium silicate solution on the surface of an expandedpolystyrene particle, and irradiating microwaves to the coating toheat-bond the sodium silicate to the polystyrene. This technology hasdisadvantages in that the coating of the sodium silicate is poor inwater resistance and expensive equipment is required for the microwaveirradiation.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide anexpanded polystyrene that can be produced using conventional moldingequipment without the need for additional expensive equipment anddeveloped into various functional products superior in flameretardation, fire resistance, antibacterial properties, waterproofness,aromatic properties, coloration properties, etc.

The object of the present invention can be achieved by coating thesurface of expanded polystyrene particles with a functional coatingcomposition to form a functional skin layer inside the particles,followed by molding. The functional coating composition used hereincontains at least one functional additive, and a polyvinyl acetate resinwith high affinity to the expanded polystyrene particles andlow-temperature melt bonding property so as to be suitable for steammolding.

In accordance with one aspect of the present invention, there areprovided expanded polystyrene particles consisting of an inner expandedpolystyrene layer and a functional skin layer wherein the inner expandedpolystyrene layer is formed by heating and expanding expandablepolystyrene beads or pellets, and the functional skin layer is formed bycoating the surface of the inner expanded polystyrene layer with afunctional coating composition containing 10˜99 wt % of a vinyl acetatebased polymer and 0.1˜90 wt % of at least one functional additive.

In accordance with another aspect of the present invention, there isprovided a process for producing the expanded polystyrene particles witha functional skin layer, comprising the steps of:

heating and expanding expandable polystyrene beads or pellets to produceexpanded polystyrene particles;

applying a functional coating composition to the surface of the expandedpolystyrene particles, the functional coating composition being preparedby mixing or dissolving at least one functional additive with a vinylacetate based polymer solution to form a functional skin layer; and

adding a release agent to the expanded polystyrene particles whosesurface is coated with the functional coating composition, to separatethe expanded polystyrene particles having the functional skin layer intoindividual particles, and drying the separated particles.

In accordance with another aspect of the present invention, there isprovided a process for manufacturing the functional expanded polystyrenemolded product comprising the steps of introducing the expandedpolystyrene particles having a functional skin layer into a molder, andapplying high-pressure steam to the molder to bond the expandedpolystyrene particles with each other.

In accordance with yet another aspect of the present invention, there isprovided a functional expanded polystyrene molded product made of theexpanded polystyrene particles with functional skin layer according tothe present invention.

A more detailed explanation concerning the structure of the expandedpolystyrene particles having a functional skin layer according to thepresent invention will be given below. The expanded polystyreneparticles having a functional skin layer are spherical particles havinga skin-core structure wherein the overall diameter of the expandedpolystyrene particles is between about 1 mm and about 30 mm, thediameter of the expanded polystyrene particles constituting the innercore layer is between about 0.999 mm and about 29.999 mm, and thethickness of the outer skin layer is between about 1 μm and about 100μm. The expanded polystyrene particles constituting the core layeraccount for 5˜99 wt %, the functional skin layer accounts for 1˜95 wt %,and other residues account for 5 wt % or less, based on the total weightof the expanded polystyrene particles.

The expanded polystyrene particles constituting the core layer includethose previously known in the art. The components and productionprocesses are as explained in the above prior art.

On the other hand, the functional skin layer is formed by coating thesurface of expanded polystyrene particles with a functional coatingcomposition containing a vinyl acetate based polymer solution and atleast one functional additive, followed by separating (to individualparticles) and drying. The vinyl acetate based polymer solution isprepared by dissolving 3˜80 wt % of a vinyl acetate based polymer in asolvent. The vinyl acetate based polymer can be a vinylacetatehomopolymer, or a copolymer of vinyl acetate and at least one monomerselected from: vinyl esters, such as vinyl caproate and vinyl stearate;acrylic esters, such as ethyl acrylate, butyl acrylate and octylacrylate; fumaric acid esters, such as dibutyl maleate; carboxylicacids, such as maleic acid, acrylic acids and itaconic acid; vinylalcohols; butadienes; and caprolactones; or a mixture or a blendthereof. The vinyl acetate based polymer has a degree of polymerization(DP) of 10˜100,000. It is preferred that the content of the vinylacetate monomer in the vinyl acetate based polymer is 55% or more.

Examples of suitable solvents to prepare the vinyl acetate based polymersolution include water, and organic solvents such as alcohols, esters,ketones, carboxylic acids, aromatics, and halogenated hydrocarbons. Itis preferred to select a solvent having relatively high volatility andreduced human toxicity, particularly, minimally dissolving or erodingthe surface of expanded polystyrene particles. In this respect, alcoholsare preferred. The concentration of the resin component is determinedwithin the range defined above, taking into account the adhesion to thesurface of the expanded polystyrene particles and workability uponhandling.

The functional additive can be added for intended functions withoutparticular limitations so long as it is readily dissolved or dispersedin the vinyl acetate based polymer solution and does not erode ordissolve the surface of the expanded polystyrene particles. Examples ofsuch additives include expanding agents, nucleating agents, lubricants,antioxidants, heat stabilizers, ultraviolet stabilizers, biostabilizers,fillers, reinforcing agents, plasticizers, colorants, impact-resistantagents, flame retardants, antistatic agents, cross-linking agents,fluorescent whitening agents, thermal conductivity-imparting agents,electrical conductivity-imparting agents, permeability modifiers,magnetism-imparting agents, surfactants, stabilizers, excipients, drugs,solvents, hardeners, desiccants, fortifying agents, flavoring agents,antibacterial agents, etc. These additives may be added alone or incombination as a mixture of two or more agents compatible with eachother.

In particular, when a flame retardant, such as antimony trioxide, aphosphoric compound, boron, boric acid or aluminum oxide, is added, akind of fire wall surrounding the surface of the expanded polystyreneparticles is built, which prevents the spread of a fire to sites notdirectly reached by the flame and maintains the overall shape of theskin layer acting as a skeleton unchanged, leading to a very effectiveflame-retardant expanded polystyrene product.

The vinyl acetate based polymer solution containing the functionaladditive is uniformly applied to the surface of the expanded polystyreneparticles. At this step, if the viscosity of the polymer solution islow, it is advantageous to stir the expanded polystyrene particles whilethe polymer solution is sprayed on the surface of the particles.Meanwhile, if the polymer solution is highly viscous, the expandedpolystyrene particles can be mixed with the polymer solution in a mixerwith stirring to apply the polymer solution to the surface of theparticles.

The application of the vinyl acetate based polymer solution containingthe functional additive to the expanded polystyrene particles may causethe polystyrene particles to be agglomerated due to the viscosity of thepolymer solution, which makes it difficult to manufacture a moldedproduct from the expanded polystyrene particles. Therefore preferably,the polymer solution is uniformly applied to the surface of the expandedpolystyrene particles, followed by the steps of separating and drying,to produce the final expanded polystyrene particles having thefunctional skin layer.

As the release agent used for separating, there may be used a liquidmaterial or a solid powder different from the solvent used to preparethe vinyl acetate based polymer solution. When the solid powder is used,the moldability of the expanded polystyrene particles is degraded anddust is created during drying. When the liquid material is toolipophilic, it is more compatible with the polystyrene than with thevinyl acetate based polymer, causing the separation of the polystyrenefrom vinyl acetate based polymer. Accordingly, the use of excessivelylipophilic liquid materials should be avoided. Thus, preferred releaseagent should be more or less hydrophilic liquid type material such thatit can be uniformly applied to the exterior surface of the vinyl acetatebased polymer, and should remain until the solvent of the polymersolution is appropriately removed such that it can. Examples of suitablerelease agents include, but are not limited to, hydrophilic liquidmaterials, such as water, ethylene glycol and glycerin, containing twoor more hydroxyl groups (—OH) in their molecular structure, and siliconeoils. These release agents can be used alone or as a mixture of two ormore thereof. The release agent is used in an amount of 1˜40 wt % of thevinyl acetate based polymer. The amount of the release agent used isproperly selected depending on the surface area of the expandedpolystyrene particles and the kind of the functional coating compositionconstituting the skin layer.

After the release agent is uniformly added, the mixture is dried withstirring to separate the expanded polystyrene particles into individualparticles. Drying is carried out in hot air at 100° C. or lower withstirring. Alternatively, the drying may be carried out in a drier at100° C. or lower with stirring, or may be carried out under reducedpressure. For better workability, a combination of vacuum drying andheating is most effective.

The functional skin layer thus formed contains 10˜99 wt % of the vinylacetate based polymer, 0.1˜90 wt % of the functional additive, and 20 wt% or less of residues of the solvent and the release agent. The contentof the functional additives is greatly dependent on functions to beimparted. For example, flame-retardants, reinforcing agents and fillersare added in large amounts, but colorants can attain desired effectsusing only small amounts. Within the range defined above, the vinylacetate based polymer can serve as a matrix capable of forming the skinlayer.

The expanded polystyrene particles having the functional skin layer arestored in a silo before use. For use, the expanded polystyrene particlesare taken out of the silo, placed in a mold having a desired shape, andmolded using high-pressure steam to manufacture a functional expandedpolystyrene molded product. This molding may be performed in accordancewith the same procedure as conventional molding processes of expandedpolystyrenes.

BRIEF DESCRIPTION THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an electron micrograph (30×) showing a cutaway portion of thesurface of an expanded polystyrene particle (C1) having aflame-retardant skin layer produced in Example 1 of the presentinvention;

FIG. 2 is an electron micrograph (400×) showing an interface between askin layer and a core layer of the cutaway portion shown in FIG. 1;

FIG. 3 is a photograph showing the initial state of a sample for aflame-retardation test, produced in Example 1 of the present invention;

FIGS. 4 and 5 are front and side photographs taken after theflame-retardation test for the sample shown in FIG. 3, respectively;

FIG. 6 is a photograph showing the results of an antibacterialperformance test for an expanded polystyrene molded product manufacturedin Example 2 of the present invention; and

FIG. 7 is an enlarged photograph showing the cross section of anaesthetic expanded polystyrene molded product manufactured in Example 3of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in more detail withreference to the following several examples of the manufacture offunctional expanded polystyrene molded products.

EXAMPLE 1 Manufacture of Flame-Retardant Expanded Polystyrene MoldedProduct

A. Preparation of Flame-Retardant Polyvinyl Acetate Solution (A1)

450 g of a polyvinyl acetate resin having a degree of polymerization of500 was uniformly dissolved in 550 g of methanol to prepare 1 kg ofpolyvinyl acetate solution. To the polymer solution was added 1 kg ofaluminum hydroxide particles having an average particle size of 7.5 μm.The resulting mixture was uniformly dispersed to prepare 2 kg of amethanolic polyvinyl acetate solution (A1) containing theflame-retardant additive.

B. Coating on Expanded Polystyrene Particles

Expandable polystyrene particles were expanded to an average of 80 fold,and dried. 2 kg of the expanded polystyrene particles were charged intoa 200-liter ribbon mixer. 2 kg of the flame-retardant polyvinyl acetatepolymer solution (A1) prepared in step A was added to the expandedpolystyrene particles with stirring at 50 rpm for one minute touniformly coat the expanded particles, yielding 4 kg of expandedpolystyrene particles whose surface was coated with the flame-retardantpolyvinyl acetate polymer solution.

C. Drying, Separating and Production of Expanded Polystyrene ParticlesHaving Flame-Retardant Skin Layer

Stirring was continued for about 10 seconds while applying hot air at60° C. to the ribbon mixer. Then, 50 g of ethylene glycol was sprayedwith stirring to allow the expanded polystyrene particles coated withthe flame-retardant polyvinyl acetate polymer solution to separate intoindividual particles. The separated particles were dried with stirringfor 3 minutes to produce expanded polystyrene particles (C1) having aflame-retardant skin layer.

D. Production of Flame-Retardant Expanded Polystyrene Molded Product

The expanded polystyrene particles (C1) having a flame-retardant skinlayer produced in step C were put in a steam molder for EPS, heated at asteam pressure of 0.6 kg/cm³ for 50 seconds, sustained for 10 seconds,and cooled to manufacture a flame-retardant expanded polystyrene moldedproduct (D1) having a density of 35 kg/m³.

E. Observation of Skin-Core Structure

For observation of the skin-core structure of the expanded polystyreneparticles having a flame-retardant skin layer produced in step C, oneparticle (C1) of the expanded polystyrene particles was selected. Aportion of the surface of the particle (C1) was cut, and then thecutaway portion was observed under an electron microscope with amagnification of 30× (see FIG. 1). This observation reveals that theexpanded polystyrene particle (C1) produced in this example is aspherical particle having an expanded structure completely coated withthe flame-retardant skin layer.

A higher magnification (400×) of the interface between the skin layerand the core layer of the expanded polystyrene particle (C1) is shown inFIG. 2. As shown in FIG. 2, the skin layer was completely adhered to theinner expanded polystyrene layer.

F. Flame-Retardation Test

The flame-retardant expanded polystyrene molded product D1 manufacturedin step D was cut into a plate-shaped sample having dimensions of 2 cm(1)×2 cm (w)×1 cm (h) (see FIG. 3), which was used for theflame-retardation test.

The sample was exposed to a 4 cm high flame from a Bunsen burner for 30seconds to conduct a flame-retardation test, and the obtained resultsare shown in FIGS. 4 and 5.

As shown in FIGS. 4 and 5, only a portion of the expanded polystyreneparticles exposed to the surface were collapsed by heating, but heat andflame were blocked by means of the skin layer and the skeleton of themolded product (D1) was maintained, confirming that the originalstructure of the molded product (D1) was unchanged.

EXAMPLE 2 Manufacture of Antibacterial Expanded Polystyrene MoldedProduct

A. Preparation of Antibacterial Polyvinyl Acetate Solution

450 g of a polyvinyl acetate resin having a degree of polymerization of500 was uniformly dissolved in 550 g of methanol to prepare 1 kg of apolyvinyl acetate solution, and then 0.2 kg of ethyl paraben was addedthereto. The resulting mixture was completely dissolved with stirringfor one hour to prepare 1.2 kg of a methanolic polyvinyl acetatesolution (A2) containing the antibacterial additive.

B. Coating on Expanded Polystyrene Particles

2.5 kg of expanded polystyrene particles coated with the antibacterialpolyvinyl acetate solution were produced in the same manner as inExample 1 (B), except that 0.5 kg of the antibacterial polyvinyl acetatesolution (A2) prepared in step A was added instead of theflame-retardant polyvinyl acetate solution (A1).

C. Drying, Separating and Preparation of Expanded Polystyrene ParticlesHaving Antibacterial Skin Layer

Drying and separating were carried out in the same manner as in Example1 to produce expanded polystyrene particles (C2) having an antibacterialskin layer.

D. Manufacture of Antibacterial Expanded Polystyrene Molded Product

The expanded polystyrene particles (C2) having an antibacterial skinlayer produced in step C were charged into a steam molder for EPS,heated at a steam pressure of 0.6 kg/cm³ for 40 seconds, sustained for10 seconds, and cooled to manufacture an antibacterial expandedpolystyrene molded product (D2) having a density of 15 kg/m³.

E. Antibacterial Performance Test

A portion of the antibacterial expanded polystyrene molded product D2manufactured in step D was ground. After 0.4 g of the ground moldedproduct and a test bacterial solution in which Staphylococcus aureus wasincubated were subjected to shaking culture at a shaking frequency of150 cycles per minute at 35° C. for 24 hours, the number of the bacteriawas counted and the bacterial decrease rate (bacteriostatic rate) wasdetermined.

After the shaking culture, the initial bacterial concentration (1.3×10⁵count/ml) of the test bacterial solution was decreased to 10 count/ml(FIG. 6).

As apparent from the results shown in FIG. 6, the antibacterial testperformed by the shake-flask method confirms a bacterial decrease of99.9% in the antibacterial expanded polystyrene molded product D2produced in this example.

EXAMPLE 3 Manufacture of Aesthetic Expanded Polystyrene Molded Product

A. Preparation of Colored Polyvinyl Acetate Solution

25 g of a polyvinyl acetate resin having a degree of polymerization of500 was uniformly dissolved in 475 g of methanol to prepare 0.5 kg of apolyvinyl acetate solution. 10 g of a black pigment was added to thepolymer solution, and was completely dissolved with stirring for onehour to prepare 0.51 kg of a methanolic black-colored polyvinyl acetatesolution (A3).

B. Coating on Expanded Polystyrene Particles

2.51 kg of expanded polystyrene particles coated with the coloredpolyvinyl acetate polymer solution were prepared in the same manner asin Example 1 (B), except that 0.51 kg of the colored polyvinyl acetatepolymer solution (A3) prepared in step A was added instead of theflame-retardant polyvinyl acetate solution (A1).

C. Drying, Separating, and Production of Expanded Polystyrene ParticlesHaving Colored Skin Layer

Expanded polystyrene particles (C3) having a black skin layer wereproduced in the same manner as in Example 1 (C), except that 250 g ofwater was used instead of ethylene glycol.

D. Manufacture of Aesthetic Expanded Polystyrene Molded Product

The expanded polystyrene particles (C3) having a black skin layerproduced in step C were charged into a steam molder for EPS, heated at asteam pressure of 0.6 kg/cm³ for 40 seconds, sustained for 10 seconds,and cooled to manufacture an aesthetic expanded polystyrene moldedproduct (D3) having a density of 15 kg/m³.

E. Observation of Cross Section of Aesthetic Expanded Polystyrene MoldedProduct

The surface of the expanded polystyrene molded product D3 manufacturedin step D was wholly black-colored. A 5 cm deep piece was cut from theexpanded polystyrene molded product D3, and then the cross section ofthe piece was observed under a microscope. The photograph is shown inFIG. 7.

As apparent from the photograph, the cross section of the expandedpolystyrene molded product (D3) had a slightly irregular shape similarto a honeycomb wherein the black-colored skin layer was formed betweenthe white expanded polystyrene particles.

In the case of a commercial block molding product manufactured bycutting the block-shaped molded product to a desired thickness, the sizeand color of the expanded polystyrene particles, and the color of theskin layer are varied, making it possible to manufacture aestheticexpandable polystyrene panels exhibiting various color effects.

INDUSTRIAL APPLICABILITY

As apparent from the above description, according to the expandedpolystyrene particles of the present invention, inherent properties ofexpanded polystyrene, e.g., light weight, thermal insulation properties,shape stability, buffering properties and sound absorption, are ensuredby the expanded polystyrene particles constituting the core layer, andat the same time, superior low-temperature bonding properties,air-tightness, waterproofness and durability are provided by thelow-softening point vinyl acetate based polymer constituting the skinlayer.

In addition, superior adhesion of the vinyl acetate based resin topolystyrene, and relatively good low-temperature adhesion properties ofthe vinyl acetate based polymer enable improvement of the physicalproperties, e.g., compressive strength, tensile strength and flexuralstrength, of the molded products of the present invention. Optionally,various functional additives, including flame retardants, waterrepellents, antibacterial agents, colorants, flavoring agents, etc., canbe added to the vinyl acetate based polymer to impart a variety offunctions to the expanded polystyrene particles of the present inventionin a simple manner. Therefore, the expanded polystyrene particles of thepresent invention can be applied to manufacture of lightweightindustrial materials, particularly construction materials, with variousfunctions.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An expanded polystyrene particle with a functional skin layercomprising: an inner expanded polystyrene layer; and a functional skinlayer, wherein the inner expanded polystyrene layer is formed by heatingand expanding an expandable polystyrene bead or pellet, and thefunctional skin layer is formed by coating the surface of the innerexpanded polystyrene layer with a functional coating composition having10 to 99 wt % of a vinyl acetate based polymer and 0.1 to 90 wt % of atleast one functional additive.
 2. The expanded polystyrene particle withfunctional skin layer according to claim 1, wherein the vinyl acetatebased polymer includes a vinylacetate homopolymer, or a copolymer ofvinyl acetate and at least one monomer selected from a group ofconsisting of vinyl esters, acrylic esters, fumaric acid esters,carboxylic acids, vinyl alcohols, butadienes, caprolactones, and amixture or a blend thereof, and wherein the vinyl acetate based polymerhas a degree of polymerization (DP) of 10 to 100,000.
 3. The expandedpolystyrene particle with functional skin layer according to claim 1,wherein the functional skin layer has a thickness corresponding to 0.003to 10% of the overall diameter of the particle, and has 1 to 95 wt % ofthe total weight of the particle.
 4. The expanded polystyrene particleaccording to claim 1, wherein the functional additive is selected fromthe group consisting of expanding agents, nucleating agents, lubricants,antioxidants, heat stabilizers, ultraviolet stabilizers, biostabilizers,fillers, reinforcing agents, plasticizers, colorants, impact-resistantagents, flame retardants, antistatic agents, crosslinking agents,fluorescent whitening agents, thermal conductivity-imparting agents,electrical conductivity-imparting agents, permeability modifiers,magnetism-imparting agents, surfactants, stabilizers, excipients, drugs,solvents, hardeners, desiccants, fortifying agents, flavoring agents,antibacterial agents, and mixtures thereof.
 5. A functional expandedpolystyrene molded product manufactured by molding the expandedpolystyrene particle with functional skin layer according to claim
 1. 6.A process for producing expanded polystyrene particles with functionalskin layer, comprising: heating and expanding expandable polystyrenebeads or pellets to produce expanded polystyrene particles; applying afunctional coating composition to the surface of the expandedpolystyrene particles, the functional coating composition being preparedby mixing or dissolving at least one functional additive with a vinylacetate based polymer solution to form a functional skin layer; andadding a release agent to the expanded polystyrene particles whosesurface is coated with the functional coating composition, to separatethe expanded polystyrene particles having the functional skin layer intoindividual particles, and drying the separated particles.
 7. The processaccording to claim 6, wherein the solvent used to prepare the vinylacetate based polymer solution is water, or an organic solvent selectedfrom alcohols, esters, ketones, carboxylic acids, aromatics, andhalogenated hydrocarbons, or mixtures thereof.
 8. The process accordingto claim 6, wherein the vinyl acetate based polymer solution includes 3to 80 wt % of a vinyl acetate based polymer based on the total weight ofthe vinyl acetate based polymer solution.
 9. The process according toclaim 6, wherein the release agent includes hydrophilic liquid materialshaving two or more hydroxyl groups (—OH) in their molecular structure,silicone oils, or mixtures thereof.
 10. The process according to claim9, wherein the hydrophilic liquid materials includes water, ethyleneglycol or glycerin.
 11. A process for manufacturing a functionalexpanded polystyrene molded product, comprising: introducing theexpanded polystyrene particles with functional skin layer produced bythe process according to claims 6 into a steam molder; applyinghigh-pressure steam to the molder to bond the expanded polystyreneparticles with functional skin layer to each other through theirfunctional skin layer; and cooling the bonded expanded polystyreneparticles.
 12. The expanded polystyrene particle with functional skinlayer according to claim 2, wherein the vinyl esters includes vinylcaproate or vinyl stearate, the acrylic esters includes ethyl acrylate,butyl acrylate or octyl acrylate, the fumaric acid esters includesdibutyl maleate, the carboxylic acids includes maleic acid, acrylicacids, or itaconic acid.
 13. The expanded polystyrene particle withfunctional skin layer according to claim 2, wherein the content of thevinyl acetate monomer in the vinyl acetate based polymer is 55 mol % ormore.